The technical field relates to a charging device for electrophotographic applications, and, in particular, to a corona cartridge for high-speed electrophotographic applications.
Office or home laser printers have become successful in the marketplace, largely due to the development of print cartridges that house various component parts, such as photoreceptors, charging devices, cleaning receptacles, and other parts, that are likely to fail over a relatively short time. If a print cartridge has enough toner for ten thousand copies, for example, the photoreceptor, charging device, and cleaning receptacle contained in the print cartridge may be designed for that life with some margin for error. After the toner is consumed, the print cartridge may be easily replaced.
However, for high-speed electrophotographic applications, such as high-speed copiers or high-speed laser printers, component parts are considerably heftier and more robust to maintain the necessary tolerances. For example, photoreceptors used in the high-speed electrophotographic applications are much larger, and corona chargers, typically used to charge the photoreceptors in the high-speed electrophotographic applications, are designed for longer life and thus heavier. A print cartridge containing all the usual replacement parts would be too heavy to pick up and maneuver and hence impractical. Accordingly, the component parts are typically replaced separately when necessary, which can be quite frequent during periods of high-volume usage. Such maintenance may need to be performed by an experienced operator.
Because of the cost, size, complexity, and possibly, the need for an experienced operator, the present high-speed electrophotographic applications have been relegated to a central copying or printing operation. If these barriers can be overcome, high-speed copying or printing maybe more successfully marketed and widely distributed. One objective for high-speed electrophotographic applications is to decrease user intervention and prolong the period between major maintenance, so that less-skilled staff can tackle a high-speed, nearly always-on publishing system, so long as the experienced operator does the rare major maintenance.
A typical corona charger consists of one or more wires encased in a shield with one open side facing a photoreceptor. During operation, a high voltage is placed on the wires, while the shield is kept near ground. A metal grid separating the wires and the photoreceptor may be used to set the photoreceptor charge voltage. In high-speed electrophotographic applications, the corona charger can be designed with a spooled wire rather than a single wire, effectively increasing the period between user interventions by approximately a ratio between the spooled wire length and the single wire length, provided that the spooled wire does not break. As the wire wears, the spool is automatically unwound to reveal a new unused section of corona wire.
However, wire coronas in general have a serious drawback. A corona charger produces a considerable amount of ozone, which may damage the photoreceptor and is a health hazard if allowed into an inhabited environment. Ozone emission is particularly acute with negative coronas that are used in nearly all printers, which emit an order of magnitude more ozone than positive coronas. Unfortunately a large majority of printers require negative charging.
Ions that charge the photoreceptor are created by air breakdown near the corona wire. Negative coronas experience breakdown sporadically along the wire length, creating pockets of high charge density interspersed with regions of low or zero charge. In order to produce sufficient charge everywhere, the input current must be increased significantly so that the corona wire will experience breakdown along its entire path. Ozone production increases proportionally with the level of input current. Accordingly, although the spooled-wire charge coronas operate well in high-speed electrophotographic applications, and far extend the life of a single wire, the drawback includes deterioration of images over time and/or increased health and environmental hazard.
Charge rollers have also been used to circumvent the ozone problem while maintaining uniform charging. A charge roller operates by relatively uniform micro breakdowns along its length, reducing the need for excess input current and the accompanying ozone emission. However, because the charge rollers are not sufficiently fast and robust for high-speed electrophotographic applications, charge rollers are limited to low-speed electrophotographic applications.
Some corona chargers do create uniform charging without increased ozone production and can be considered for high-speed electrophotographic applications. These chargers are comb-like devices, such as saw-tooth or pin-electrode charging devices, that place a plurality of uniformly spaced sharp points along the length. Each of these sharp points increases the likelihood of corona breakdown, so that the entire device can experience uniform breakdown at a relatively low current, in contrast to the wire-type negative-charging devices. With reduced input current, the amount of undesirable ozone generated can be significantly reduced to about one-tenth of that generated by wire-type charging devices.
However, unlike wire-type charging devices, comb-like charging devices are bulky and rigid, and cannot easily be wound into a spool or a bobbin to be pulled out whenever they wear out, as is done for the spooled-wired corona charging devices. Accordingly, increased maintenance effort may be required when operating with comb-like charging devices.
A corona cartridge extends the lives of comb-like charging devices within high-speed electrophotographic applications without active intervention by automatically advancing a new saw-tooth charging device when an old charging device wears out. The corona cartridge may include a comb-like corona charging device, such as a saw-tooth or pin-electrode corona charging device, positioned in a shield case and electronically connected to operate with a photoreceptor for copying or printing, and one or more excess corona charging devices stored in the corona cartridge. The stored excess corona charging devices have the same functionality as the electronically connected corona charging device, and may be advanced automatically to replace the electronically connected corona charging device when the charging device wears out.
In one embodiment, the one or more excess comb-like corona charging devices may be stored on a shaft positioned above the shield case and capable of being lifted an rotated for replacement. In another embodiment, the one or more excess comb-like corona charging devices may be stored in a dispenser that is positioned above the shield case. In yet another embodiment, the number of excess corona charging devices (including the electronically connected corona charging device) may be tailored to last as long as the photoreceptor typically used in the high-speed electrophotographic applications, which may run many months even in high-use operations. Accordingly, by matching total lives of the excess corona charging devices (including the electronically connected corona charging device) to that of the photoreceptor, the high-speed electrophotographic applications may need to be serviced only when the photoreceptor wears out, thus significantly reducing the maintenance frequency without the side effect of increased ozone production, as in the case of wire-type corona charging devices.